Riparian, or streamside, areas are critical
habitat for many plants and animals in the arid West. Livestock grazing is the
leading cause of riparian degradation. Impacts to vegetation, stream hydrology,
and geomorphology can separately or synergistically affect stream functioning
and many wildlife species. Thus, riparian restoration, including the removal
of livestock, must be a high priority for the conservation of biodiversity.

J. Boone Kauffmanis professor of ecosystem
sciences in the Department of Fisheries and Wildlife, Oregon State University,
Corvallis. He studies the ecology and restoration of riparian zones in the arid
West, as well as tropical forest ecology in Central and South America, and has
written more than a hundred scientific papers on natural ecosystems. He grew
up on the West Texas plains and holds a Ph.D. degree in forest ecology from
the University of California at Berkeley, as well a B.S. degree in range management
and an M.S. degree in range ecology.

Riparian zones are a unique wetland environment adjacent
to rivers or streams. People have long recognized that riparian zones and rivers
are the lifeblood of the western landscape, being more productive and home to
more plants and animals than any other type of habitat. Scientists refer to
riparian zones as hotspots of biodiversity, a characterization that is particularly
apparent in arid and semiarid environments, where such zones may be the only
tree-dominated ecosystems in the landscape. The presence of water, increased
productivity, favorable microclimate, and periodic flood events combine to create
a disproportionately higher biological diversity than that of the surrounding
uplands.

Cattle graze in a wet meadow along
Blacktail Creek, Beaverhead National Forest, Montana. Streamside vegetation
is cropped low, parts of the stream bank are bare, and other parts are sloughing
into the creek.

In the Intermountain West and Great Basin, about 85
percent of native animal species are dependent on riparian zones for all or part
of their life cycles. In these same riparian zones, more than 100 plant species
commonly can be found on a single gravel bar of about 150 feet in length. In Oregon
and Washington, about 71 percent of the native animal species utilize riparian
zones. Given that riparian areas make up only 0.5 to 2 percent of the landscape,
their value in terms of biological diversity is incomparable.

Healthy riparian zones are of special importance to native fish, aquatic insects,
and other stream-dwelling organisms. Particularly in headwater areas, most of
the nutrients and energy used by aquatic organisms come from riparian zones--either
plant materials that fall into the stream or nutrients dissolved in groundwater
flows. Riparian zones are also the source of large pieces of wood that provide
important in-stream habitat. Riparian vegetation gives shade over creeks, strongly
influencing water temperature and thereby the distribution of coldwater species
such as bull trout and other salmonids. Roots bind soil together and create resistance
to stream erosion, resulting in complex habitat features such as overhanging banks,
deep pools, and clean gravels. Finally, riparian zones are important in influencing
water quality through nutrient uptake, chemical transformation (such as the conversion
of nitrogen compounds into forms more useful for a variety of plant and animal
species), and the mechanical filtering of sediments when flood waters flow high
over stream banks.

Many of the same attributes of riparian zones that result in high productivity
and high biodiversity are of great economic value to human society. Unfortunately,
many current uses of riparian corridors and wetlands by society do not correspond
with preservation of these places as wildlife habitats or as providers of important
natural services, such as the reduction of flood velocity and intensity. Broad
floodplains formed along streams through the millennia have been productive not
only because of their complex wildlife habitats and linkages to the aquatic biota
but also because of their nutrient-rich soils. In fact, although the best lands
for tilled agriculture, livestock forage, and timber growth are riparian zones
and wetlands, these same activities, along with a variety of others, have been
conducted in such an abusive fashion as to diminish greatly the value of riparian
and stream ecosystems, from both utilitarian and ecological viewpoints.
A multitude of land uses show a lack of respect for, or ignorance of, the value
of healthy and vigorous riparian zones and have resulted in the deterioration
of not only riparian areas, but the entire landscape. In general, land abuses
that have degraded riparian zones include logging, water diversion for irrigation
or municipal uses, mining, roads, channelization, urbanization, industry, and
agriculture. In the western United States, it is likely that livestock grazing
has been the most widespread cause of ecological degradation of riparian/stream
ecosystems. More riparian areas and stream miles are affected by livestock grazing
than by any other type of land use.

Livestock, especially cattle, prefer riparian zones for many of the same reasons
that so many species of wildlife use them: high plant productivity, proximity
to water, favorable microclimate, and level ground. As much as 81 percent of the
forage removed by livestock within a grazing allotment can come from the 2 percent
of land area occupied by the riparian zone. Without controls on animal numbers,
timing, and duration of use, cattle can rapidly and severely degrade riparian
areas through forage removal, soil compaction, stream bank trampling, and the
introduction of exotics. These factors have been defined as the direct effects
of domestic livestock grazing on ecosystems.

Through time, the direct effects of livestock can have many additive or even synergistic
impacts that dramatically change the structure, function, and composition of the
riparian zone. Of particular importance are the effects of livestock on streamside
forests of cottonwood, aspen, and willow. The highest densities of breeding songbirds
in the West are found in these habitats. Long-term overgrazing can eliminate these
stands, which are of inestimable value as centers of biological diversity. In
the short term, herbivory can depress both plant growth and reproductive output.
Depressing the vigor of native plant species, along with increased soil disturbance
due to livestock trampling, facilitates the spread of exotic weeds. Herbivory
also causes a corresponding decline in the root biomass of riparian vegetation.

This stream in northern New Mexico has become entrenched.
Over time, grazing and trampling of the soils and banks by livestock have
caused the stream to widen and cut downward. Typical results of this stream
degradation process include lowered water table, drier soil in the zone
adjoining the waterway, and riparian-type plants (such as willows) gradually
replaced by more drought-resistant plants (such as sagebrush).

At stream edges, the combination of root loss and trampling
weakens and collapses banks. Bank loss and the resulting sediment loads contribute
to downcutting, channel widening, and degradation of water quality and fish
habitats. As the channel downcuts, overbank flows cease, and subsurface water
exchange between stream and floodplain is lost. Floodplain forests evolved to
grow and develop in the environment created by large floods. By altering or
eliminating the natural flood regime, channel downcutting impedes or halts the
development of multi-layered, multi-aged--or "gallery"--forests, such
as those composed of cottonwood trees and willows, along with other riparian
plants. Loss of the riparian forests negatively affects not only the terrestrial
wildlife, but the aquatic biota as well. Loss of shade and organic inputs from
riparian vegetation results in increased stream temperature, altered water quality,
and a change in composition and abundance of the aquatic biota.

Although occupying a small portion of the landscape, riparian zones are keystone
ecosystems because of their high level of biodiversity and provision of other
ecosystem services. The restoration of riparian zones would yield many positive
benefits, including the return of flood events to something resembling their
natural patterns. Because riparian plants have adapted to survive frequent floods
and other natural disturbances, they often show great resilience after the cessation
of human activities that are causing degradation. Such removal of harmful activities
is termed passive restoration, and in the arid West, the most significant act
of passive restoration would be the removal of grazing livestock. Logically,
passive restoration should be implemented first, and its effectiveness assessed,
before the initiation of more active measures, such as structural modifications
and reintroductions of species.

Among the greatest barriers to effective riparian recovery are political and
social factors. Land and river managers have often been limited to, or limited
themselves to, band-aid approaches that do not address the real causes of degradation.
For example, salmon have continued to decline in the Columbia Basin of the Pacific
Northwest, despite the input of billions of dollars for restoration projects
and mitigating measures, because, among other reasons, livestock continue to
degrade riparian zones. A prominent and popular project on public lands in the
Columbia Basin has been the installation of artificial structures in smaller
streams, in an attempt to re-create aquatic habitat that has been lost to decades
of poor resource management. However, artificial stream structures can be expensive
and often are sited and constructed poorly.

In many cases, the most effective, cheapest, and simplest approach to restoring
these river courses would be to halt grazing damage and allow the streams to
recover their own natural vegetative and morphological characteristics over
time. But it can be extremely difficult politically for managers to make such
decisions. And restoration results can take a long time to appear, whereas political
demands arise much more rapidly. Yet, given the inestimable natural values that
arise from healthy riparian zones, a long-term commitment to riparian restoration,
preservation, and sustainable management should receive high priority. The reduction
or removal of livestock from vital riparian and wetland habitats throughout
the West needs to be given serious consideration by all those concerned about
ecosystem health.